Single fire glazed ceramic body



United States Patent Oifice 3,539,387 Patented Nov. 10, 1970 3,539,387SINGLE FIRE GLAZED CERAMIC BODY George D. Kelly and David L. Dean,Zanesville, Ohio, assignors to Ferro Corporation, Cleveland, Ohio NoDrawing. Filed Sept. 19, 1967, Ser. No. 668,937 Int. Cl. C04b 41/06 US.Cl. 117-123 13 Claims ABSTRACT OF THE DISCLOSURE The combination of ahigh strength alumina-nepheline syenite-clay body fired to zero Waterabsorption, having a glaze applied thereto prior to firing said body,said glaze matured concurrently with said body, said glaze bodyparticularly adaptable to highway road markers and lane dividers.

BACKGROUND OF THE INVENTION There are two types of highway markers orlane dividers, reflective and non-reflective types.

Non-reflective road markers consist of a round or square button ofapproximately 4 inches in lateral dimension by approximately high. Thesemarkers are made from plastic or conventional clayflint-feldspar ceramicformulations with conventional ceramic glazes. Th plastic non-reflectingroad markers are blackened by tire marks from moving vehicles andeventually become so discolored that they are diflicult to see.Conventional glazed ceramic road markers are not discolored by tiremarks, but it has been found that, when they are mounted, particularlyon asphalt roads in hot weather, the road surface is not suflicientlyrigid to prevent slight deflection of the markers upon tire impact. Thisflexing action tends to rupture the conventional ceramic markers andtheir life is thereby limited. It appears that the ideal marker would bea ceramic marker which does not discolor from tire impact and which isconsiderably stronger than conventional markers now in use.

Plastic reflective road markers have been tried consisting of amethyl-methacrylate plastic shell, into which a prismatic typereflecting surface has been molded. As a reflector, this type of markeris sufficiently effective; however, since it is made of plastic it hasbeen found that its service life on the road is quite limited, due toabrasion and breakage from tire impact. For reflecting type roadmarkers, it appears that the ideal marker would consist of a glazed,ultra strong ceramic base into which a plastic reflecting surface hasbeen set.

The key to producing both the non-reflecting and the reflecting typeroad markers of ideal quality is in the de velopment of an ultra strongglazed ceramic base. The object of this invention is to provide such aglazed ceramic base for both reflecting and non-reflecting ceramic roadmarkers.

Conventional ceramic road markers may be manufactured from mixtures ofclay, flint, and feldspar. Upon firing of such bodies to vitrification,or the point of zero water absorption, a road marker having a modulus ofrupture in the range of 46,000 p.s.i. is obtained. We have found that,if a road marker is made from the composition of this invention andfired to vitrification at Cone 12, the resulting product has a modulusof rupture in the range of 8l3,000 p.s.i. Thus, it can be seen that thenew road marker composition is 2. to 3 times stronger than conventionalclay-flint-feldspar road markers having a modulus of rupture on theorder of 4-6,000 p.s.i.

In the manufacture of conventional ceramic road markers, the usualprocedure is to press the so-called green or unfired road marker andthen to apply an unfired ceramic glaze by spraying or by dipping. Thebody and glaze combination is then fired simultaneously to produce avitrified ceramic body which is covered by a fully matured ceramicglaze. However, in attempting to produce a glazed road marker from thenew high strength ceramic body of this invention by this so-calledone-fire technique, it was found that, during firing, the body waswarped or badly distorted. The cause of this distortion during firing isnot fully understood; however, a theory concerning its probable causehas been evolved.

Although we have no wish to be bound thereby, we believe the theory tobe as follows: When any ceramic body is fired to the point ofvitrification, it will be noted that there is a large decrease in lineardimensions of the body. This decrease in size is commonly referred to asfiring shrinkage. It is well known that when a ceramic body is heated,it does not shrink appreciably until a temperature of to 200 F. belowits ultimate firing temperature is reached. From this point until thefinal maturing temperature is reached, the ceramic body shrinks rapidly.

In the manufacture of conventional ceramic road markers, usingconventional ceramic glazes, it appears that the melting of the glazesoccurs at such a point in the firing cycle that the firing shrinkage ofthe ceramic body is not interfered with and the body and glaze shrinktogether to produce a dimensionally accurate road marker. When commonceramic glazes are applied to the new high strength road marker body,and an attempt is made to produce a road marker by the single-fireprocess, it appears that the glazes melt or react with the ceramic bodybefore the body begins its period of rapid shrinkage. The melted glazeor reaction layer which is formed between the glaze and the surface ofthe ceramic body, does not shrink uniformly with the body during itsperiod of rapid firing shrinkage. The stresses which are set up in thesystem during this period cause the road marker to distort.

It is known that the high strength body of this invention can be firedto vitrification, a conventional ceramic glaze applied and the glazematured in a second firing operation. The economic disadvantages ofusing a twofire process, however, are obvious. It would be highlyadvantageous to be able to employ a single-fire process in themanufacture of high strength ceramic road markers.

It has been found that the glaze composition of this invention can beapplied to the unfired high strength ceramic body of this invention, andthe body and glaze fired to complete maturity in a one-fire process.

It is submitted that the combination of the instant novel high strengthbody and glaze composition represents a unique approach to theeconomical manufacture of high strength glazed ceramic road markers.

It is therefore an object of this invention to provide a high strength,single fired, glazed ceramic body.

It is another object of this invention to provide a glaze adaptable tobe fired on a high strength green body at Cones 11 to 13.

SUMMARY OF THE INVENTION Broadly stated, the body composition of thisinvention falls within the following range:

Percent by wt.

Alumina 20-50 Clay 20-50 Nepheline syenite 18-32 The calculatedcompositional oxide range of the foregoing being:

Percent by wt.

Ignition loss and impurities 1.5

The preferred range of body composition being:

Percent by wt.

The calculated compositional oxide range of the foregoing being:

Percent by wt.

SiO 28-36 Ignition loss and impurities 1.5

The preferred body composition being:

Percent by wt.

325 mesh alumina 45 400 mesh nepheline syenite 25 Ball clay 30 Thecalculated compositional oxide range of the foregoing being:

Percent by wt.

A1 0 62.6 SiO 32.1 N320 2.9 K 0 1.3 Ignition loss and impurities 1.

The glaze composition (raw) of this invention falls within the followingrange:

Percent by wt.

Alumina 0-20 Clay 5-35 Nepheline syenite 65-95 Milled zircon 8-14 Talc0-6 The calculated compositional oxide range of the foregoing being:

Percent by wt.

The calculated compositional oxide range of the foregoing being:

Percent by wt. SiO 54-61 A1 0 20-26 Na O 6-9 K 0 2-4 MgO 0.3-1.5 ZrO 5-7Ignition loss and impurities L. 1.5

The preferred glaze composition being:

Percent by wt.

Nepheline syenite 79.3 Plastic kaolin 8.8 Milled zircon 8.8 Talc 3.1

The calculated compositional oxide range of the foregoing being:

Percent by wt.

SiO 58.5 A1 0 22.3 N320 8.0 K 0 3.3 MgO 1.0 ZrO 5.9 Ignition loss andimpurities l.0

In the preferred body composition, minus 325 mesh alumina, minus 400mesh nephelinc syenite, and ball clay were used. Kaolin clay can besubstituted for at least 50% of the ball clay. It is known that feldsparcan be substituted for part or all of the nepheline syenite, but suchbodies are more refractory than the preferred composition and must befired to a somewhat higher temperature depending upon the amount offeldspar employed. Also, it is not necessary to utilize alumina andnepheline syenite of such fine particle size. Coarser starting materialscould be employed, but this would require grinding of the body prior tofabrication of road markers.

DESCRIPTION The preferred body of this invention was batch weighed, andmixed according to conventional procedures with water to provide amoisture content of from about 8 to 14 weight percent, based upon theweight of the unfired body, after which, utilizing conventional methods,the body was pressed into a disk-shaped road marker utilizing aconventional ceramic press at pressures of approximately 1000 p.s.i.

However, it is to be understood that the body of this invention isadaptable to be either slip cast or ram pressed, with appropriatealteration in water content.

The preferred glaze composition, milled by conventional methods to theappropriate specific gravity was applied to said road marker by either asplash technique at a specific gravity of 1.70 to 1.72, or by sprayingor dipping using conventional methods.

The glaze may be applied to the green body either following completedrying thereof or it may be applied following pressing and partialdrying to provide a relatively dry surface to accept the glaze.

For spraying, the glaze slip was adjusted to 1.64 specific gravity.Following glazing and drying, the green glazed ceramic road marker wasfired in a conventional kiln to Cone 12, although Cone 11 to Cone 13inclusive would provide equally good results.

Firing at this range produced a body of zero water absorption having amodulus of rupture of at least 8000 p.s.i., said body covered with anextremely hard, abrasion resistant glazed surface, all accomplished in asingle fire.

Although it might be possible to reformulate a glaze using other rawmaterials to provide a glaze having essentially the same oxide analysis,we believe such glazes would likely not work on the body of thisinvention since the melting characteristics of any substitute glazewould be sufiiciently different from those of the glaze compounded fromour raw materials that such substitute glaze would likely be totallyincompatible with our high strength body from both the fusion standpointas well as its use, utility, and durability.

Conventional porcelain glazes, as known to the ceramic art, were foundto react adversely with the body of this invention. Hundreds of glazesof the conventional porcelain type, glazes reformulated to have the sameoxide analysis as the subject glaze of this patent, and many otherglazes were investigated and all those glazes having satisfactorysurface appearance were found to be incom patible with the body of thisinvestigation.

This incompatibility is characterized by a reaction between the body andthe glaze which causes deformation Of the glaze-body combination.Incompatible glazes, ap-

plied to the body of this invention, result in a fired combination inwhich the glazed surface of the road marker assumes a smaller radius ofconvexity, and the bottom of the road marker becomes concave, ratherthan remaining fiat as is desired. It is thought that this deformationis due to the melting of at least a portion of the glaze constituentswhile the body is still in a fairly highly porous condition. The portionof the melted glaze, or melted glaze constituents, is thought to thenenter that portion of the body adjacent to the glazed area, causing thisportion of the body to assume a dense and vitrified character while theremaining portions of the body are still in a relatively highly porouscondition.

As the firing continues, the remaining, unvitrified portion of the bodycontinues to shrink to a considerable degree, while that portion whichhas been vitrified by glaze constituents shrinks little, if any. The netresult is that the portion of the body adjacent to the glaze shows alower firing shrinkage than the portion of the body which is removedfrom the glaze. This results in the glazed surface of the road markerassuming a shorter radius of convexity, while the bottom, unglazedsurface of the road marker assumes concavity.

It was found that conventional porcelain glazes and other lessconventional glazes could be reformulated so as to produce a glaze Whichmelted very late in the firing cycle, at a time when the body wasessentially vitrified. These glazes resulted in road markers whichshowed no deformation, but, because of the refractory nature of theseglazes, the glaze surface was characterized by one or more defects suchas pinholes, dullness, or waviness.

And while we produce, by pressing, a body having a modulus of rupture of8-l3,000 p.s.i., it is contemplated that if we resorted to slip castingor ram pressing, the body of this invention would provide substantiallyhigher modulus of rupture values.

While it is known in the ceramic art generally to produce, utilizing asingle fire, glazed bodies such as wall tile and sanitary ware, itshould be pointed out that glazed tile are normally not fired tovitrification or zero water absorption as is our body, and tile arefurthermore matured at temperatures considerably below Cone 12. Sanitaryware is produced from clay-flint-feldspar type bodies and glazes whichare similar in composition to those used to manufacture conventional lowstrength ceramic road markers.

Neither tile nor sanitary ware bodies exhibit modulus of nlpture valuesas high as the body of this invention, nor could the glaze of thisinvention be utilized on either tile or sanitary ware bodies as it isfar too refractory, and vice versa.

Nor do we believe that our body would be adaptable to tile or sanitaryware production inasmuch as the large amount of alumina in our bodymakes it far too costly for this purpose. Furthermore, although ourrelatively simple bodies can be produced by casting, the complexsanitary ware shapes could be cast only with difficulty from our bodyinasmuch as the high level of alumina tends to reduce its castabilityfor the complex shapes.

Too, since tile is not fired to vitrification it does not present thelarge degree of firing shrinkage encountered with our body, hence theproblem of distortion and warpage by glaze and body shrinkagedifferential would not previously have been encountered in theserelatively heavy clay bodies.

And, while it is true, as widely practiced, that various other glazescould be applied to our high strength body in a two fire process (bisqueand glost), this presents one of the very problems which this inventionis designed to solve, i.e., the need for twice firing the relativelythick, heavy shapes of this invention.

Having thus described and illustrated our invention, it is set forth inthe following claims which are to be construed in the light of theUnited States statutes and decisions in such a manner as to give themthe broad range of equivalents to which they are entitled.

Percent by wt.

Alumina 20-50 Clay 20-50 Nepheline syenite 18-32 the glaze thereon,prior to firing having the following composition:

Percent by wt.

Alumina 0-20 Nepheline syenite 65-95 Clay 5-35 Milled zircon 8-14 Talc0-6 2. The glazed body of claim 1 wherein the body prior to firing hadthe composition:

Percent by wt.

-325 mesh alumina 45 400 mesh nepheline syenite 25 Ball clay 30 and theglaze thereof prior to firing had the composition:

Percent by wt Nepheline syenite 79.3

Plastic kaolin 8.8 Milled zircon 8.8 Talc 3.1

3. The glazed, single fired ceramic body of claim 1, the glaze thereon,prior to firing, having the following composition:

Percent by wt.

Alumina 0-5 Nepheline syenite 75-85 Clay 5-15 Milled zircon 8-10 Talc1-4 4. The glazed, single fired ceramic body of claim 1, the bodythereof, prior to firing, having the following composition:

Percent by wt.

Alumina 40-50 Clay 25-35 Nepheline syenite 20-30 5. The glazed body ofclaim 1 wherein the body prior to firing had the composition:

Percent by wt.

-325 mesh alumina 45 400 mesh nepheline syenite 25 Ball clay 30 6. Theglazed body of claim 1 wherein the glaze thereon, prior to firing, hadthe following composition:

Percent by wt. Nepheline syenite 79.3

Plastic kaolin 8.8 Milled zircon 8.8 Talc 3.1

7. A glazed, single fired ceramic body having a minimum modulus ofrupture of 8000 p.s.i. said body and glaze having been fired to maturitysimultaneously, said body, prior to firing, having the following oxidecomposition:

Percent by wt.

A1203 58-67 sio 28-36 Na O 2-4 K20 1-2 7 the glaze thereon, prior tofiring having the following oxide composition:

Percent by wt.

8. The glazed body of claim 7 wherein the body prior to firing had theoxide composition:

Percent by wt.

A1203 626 sio 32.1 N6 2.9 K20 1.3

and the glaze thereof prior to firing had the oxide composition:

Percent by Wt.

SiO 58.5 A1 0 22.3 Na O 8.0 K 0 3.3 MgO 1.0 zro 5.9

9. The glazed, single fired ceramic body of claim 7, the glaze thereon,prior to firing, having the following oxide composition:

Percent by wt.

SiO 47-59 A1 0 2 l-43 Na O 6-10 K 0 24 M g0 0-2 ZrO -1 0 10. The glazed,single fired ceramic body of claim 7, the body thereof, prior to firing,having the following oxide composition:

Percent by Wt.

A1203 45-67 sio 2343 N320 24 K 1-2 11. The glazed, single fired ceramicbody of claim 7,

8 said body, prior to firing, having the following oxide composition:

Percent by wt.

A1203 -67 sio 23 43 N320 2 4 K20 1 2 the glaze thereon, prior to firinghaving the following oxide composition:

Percent by wt.

sio 47 59 A1203 2143 N320 610' K20 2-4 M g0 02 2:0 5-10 12. The glazedbody of claim 11 wherein the body prior to firing had the oxidecomposition:

Percent by Wt.

A1203 626 sio 32.1 N5 0 2.9 K20 1.3

13. The glazed body of claim 11 wherein the glaze thereon, prior tofiring, had the following oxide composition:

Percent by wt.

sio 53.5 A1203 22.3 N320 3.0 K20 3.3 MgO 1.0 zro 5.9

References Cited UNITED STATES PATENTS 2,053,244 9/1936 Turk l0648 XR2,361,376 ill/1944 Athy et al. 106-48 2,370,695 3/1945 Stuft 10648ALFRED L. LEAVITT, Primary Examiner W. F. CYRON, Assistant Examiner US.Cl. X.R. 117-l25, 169

